What is the grammatical function of lā in “lā tahluk”?

Ṭarafah ibn al-ʿAbd: Ruins, Ships, Gazelle, and Beauty (Verses 1–10)

• generic-negating lā with an accusative noun
• prohibitive lā, governing a jussive imperfect
• coordinating lā joining two nouns
• an entirely expletive lā with no sense